Explosives or blasting compositions of the aqueous gel or slurry type, commonly referred to as slurry explosives or blasting agents, and referred to herein as aqueous blasting compositions, have achieved wide acceptance as commercial blasting agents owing to their low cost, safety and inherent water resistance. Aqueous blasting compositions, containing a continuous liquid phase and comprising generally an inorganic oxidizing salt, usually predominantly ammonium nitrate (AN), a thickening agent for the liquid phase in which some or all of the oxidizing salt is dissolved, a fuel and/or sensitizer and, optionally, other ingredients such as gassing and cross-linking agents, have been very successful even in water-containing boreholes due to their inherent water resistance. Another advantage of these compositions is that they are readily pumpable immediately after formulation at an elevated temperature and can therefore be pumped from a mixing chamber into a borehole for detonation. Due to the fluid nature of these compositions during pumping, essentially complete coupling with the surfaces of the borehole is achieved. If desired, the compositions can also be packaged through an extrusion apparatus such as described in U. S. Pat. No. 3,783,735.
Attempts are continually made to reduce the ingredient costs of aqueous blasting compositions in order to increase their competitiveness with non-aqueous compositions such as ANFO. A major proportion of ingredient costs is for the fuel and sensitizer ingredients. Fine, hydrophobic aluminum particles are commonly employed as both fuel and sensitizer in aqueous blasting compositions. Other fuels find substantial use as well, for example, miscible liquid hydrocarbon fuels such as ethylene glycol, formamide, etc.; sulfur; carbonaceous materials; polysaccarides; starches and others. Until recently, soluble fuels have been particularly preferred because they allow for molecular contact between fuel and oxidizer molecules which are in solution in the continuous aqueous phase of the aqueous blasting composition. This molecular contact enhances sensitivity to detonation. Ethylene glycol probably has been the most commonly used soluble fuel and aluminum particles are usually combined with ethylene glycol as additional fuel and/or sensitizer. However, this and other combinations of fuels are relatively expensive.
More recently, immiscible liquid hydrocarbon fuels have been used due to their lower cost. See, for example, U.S. Pat. Nos. 3,787,254 and 3,2788,909. A preferred immiscible fuel is No. 2 fuel oil. However, the use of an immiscible liquid fuel in an aqueous blasting composition having a continuous aqueous phase has presented problems. The major problem has been the effecting and stabilizing of a desired fine dispersion of the immiscible fuel in small droplets throughout the aqueous phase. It is found that unless a fine dispersion is maintained the sensitivity of the composition is greatly reduced. It is believed that this loss of sensitivity is due to the segregation or separation of oxidizer and fuel due to the coalescence of dispersed immiscible liquid fuel droplets. It has been observed that bulk loaded compositions can lose their sensitivity within a few hours due to coalescence and breakdown of the fuel dispersion.
Previous means have been employed to maintain a stable, fine dispersion of the immiscible fuel droplets throughout the liquid phase. Emulsifyng agents have been employed, but such agents are relatively expensive. The use of significant proportions of calcium nitrate (CN) as part or all of the oxidizer salt has been found to effect and stabilize the dispersion (U.S. Pat. No. 3,787,254). A formulation procedure involving the prethickening of the aqueous, salt-containing phase of the composition prior to the addition of the immiscible liquid fuel has also been found to effect and stabilize the dispersion (U.S. Pat. No. 3,788,909). In the present invention, it has been found that the use of a crystal habit modifier to control the crystal size of the oxidizer salt in the composition greatly increases sensitivity by maintaining a stable, fine dispersion of the immiscible liquid fuel. This effect is additive to the other means describes above of effecting and stabilizing the dispersion.
The use of crystal habit modifiers in aqueous blasting compositions is known. U.S. Pat. No. 3,397,097 discloses the use of a crystal habit modifier in a thickened aqueous inorganic oxidizer salt blasting composition containing a soluble fuel as opposed to an insoluble fuel. The modifier was used to control the size of the crystals of the inorganic oxidizer salts upon precipitation of the salts from the hot inorganic oxidizer salt solution used in formulating the compositions. It was disclosed that the crystal habit modifier, employed in combination with gas-filled cavities and soluble fuel, enhanced the sensitivity of the blasting compositions at low temperatures by keeping the salt crystals small. (Col. 5, line 20-35). All of the soluble fuels disclosed in the U.S. Pat. No. 3,397,097 patent are water-miscible fuels. The increased sensitivity resulted simply from more intimate contact between oxidizer and fuel constituents due to the reduced size and increased surface area of the oxidizer salt particles. However, when a crystal habit modifier is used in an aqueous blasting composition containing an immiscible liquid fuel, an additional surprising and unexpected result occurs.
Not only are the precipitated crystals smaller in size and larger in surface area than if the modifier were not present, which is known, but also the fine crystal structure forms in effect a matrix which maintains or stabilizes the immiscible liquid fuel droplets in a dispersed state. Thus not only does the modifier sensitize by reducing crystal size but also by acting, in effect, as a long-term dispenser of the immiscible fuel. It is found that the use of a crystal habit modifier in aqueous blasting compositions containing immiscible liquid fuels produces such a surprising impact upon sensitivity, particularly with time, that it use can mean the difference between a practicably successful and unsuccessful composition. The use of the modifier creates storage life where essentially none existed previously. The examples below illustrate this phenomenon.